Gram-Positive Cocci Overview
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Questions and Answers

What is the cellular arrangement of Staphylococci?

  • Pairs
  • Grape-like clusters (correct)
  • Chains
  • Single cells

    • Which of the following is a coagulase positive Staphylococcus?

  • Staphylococcus aureus (correct)
  • Staphylococcus hominis
  • Staphylococcus epidermidis
  • Staphylococcus saprophyticus

    • What enzyme does Staphylococcus aureus produce that is significant for clot formation?

  • Lipase
  • Protease
  • Hyaluronidase
  • Coagulase (correct)

    • Which of the following is NOT a characteristic of Staphylococcus aureus?

    <p>Motile</p> Signup and view all the answers

    What is the significance of teichoic acid found in Staphylococcus aureus?

    <p>Involved in attachment and may cause septic shock</p> Signup and view all the answers

    How is Staphylococcus aureus primarily transmitted?

    <p>Hand contact</p> Signup and view all the answers

    What distinguishes Methicillin-resistant Staphylococcus aureus (MRSA) strains?

    <p>Antibiotic resistance</p> Signup and view all the answers

    Which virulence factor is associated with causing wound infections by Staphylococcus aureus?

    <p>Collagen-binding proteins</p> Signup and view all the answers

    What is the primary cause of Scalded Skin Syndrome caused by Staphylococcus aureus?

    <p>Production of exfoliative toxins</p> Signup and view all the answers

    Which of the following symptoms is NOT typical of septic shock?

    <p>Rash</p> Signup and view all the answers

    What characterizes the systemic infections caused by Staphylococcus aureus?

    <p>Seeding of various tissues through the bloodstream</p> Signup and view all the answers

    Which toxin is specifically associated with food poisoning due to Staphylococcus aureus?

    <p>Enterotoxin B</p> Signup and view all the answers

    Which of the following infections is NOT caused by Staphylococcus aureus?

    <p>Tetanus</p> Signup and view all the answers

    What is a major consequence of the cytokine production induced by Enterotoxin B?

    <p>Stimulation of the vomiting center</p> Signup and view all the answers

    Which of the following conditions is associated with high fever and subsequent circulatory collapse?

    <p>Septic shock</p> Signup and view all the answers

    Which of the following is a characteristic of non-pyogenic skin infections caused by Staphylococcus aureus?

    <p>Includes cellulitis and impetigo</p> Signup and view all the answers

    What is a primary clinical concern associated with Staphylococcus epidermidis?

    <p>Infecting intravenous catheters and prosthetic implants</p> Signup and view all the answers

    Which characteristic is NOT true for streptococci?

    <p>They are catalase-positive</p> Signup and view all the answers

    Which group of streptococci produces a clear zone around their colonies on blood agar?

    <p>Beta-hemolytic streptococci</p> Signup and view all the answers

    What type of infections is Staphylococcus saprophyticus primarily known for causing?

    <p>Urinary tract infections in sexually-active young women</p> Signup and view all the answers

    What is the primary pathogen among the Streptococci species?

    <p>Streptococcus pyogenes</p> Signup and view all the answers

    What is the method of classification for beta-hemolytic streptococci that is based on carbohydrate antigens?

    <p>Lancefield grouping</p> Signup and view all the answers

    Which condition is often associated with Streptococcus pyogenes due to the production of erythrogenic toxin?

    <p>Scarlet Fever</p> Signup and view all the answers

    Which characteristic differentiates gamma-hemolytic streptococci from alpha and beta types?

    <p>They do not produce any hemolysis.</p> Signup and view all the answers

    What inflammation is primarily caused by Streptococcus pyogenes, especially among children?

    <p>Pharyngitis</p> Signup and view all the answers

    Which bacterium is a major cause of sepsis in neonates?

    <p>Staphylococcus epidermidis</p> Signup and view all the answers

    What role does Streptokinase play in medical treatment?

    <p>It dissolves fibrin in clots.</p> Signup and view all the answers

    What is the primary mechanism of hemolysis for beta-hemolytic streptococci?

    <p>Complete lysis of red blood cells by exotoxins</p> Signup and view all the answers

    What is a characteristic feature of necrotizing fasciitis caused by certain strains of Streptococcus pyogenes?

    <p>Massive tissue necrosis</p> Signup and view all the answers

    Which of the following is a common inhabitant of the human microbiota that can cause infections?

    <p>Streptococcus agalactiae</p> Signup and view all the answers

    What disease can arise from a throat infection with Streptococcus pyogenes?

    <p>Bacteremia</p> Signup and view all the answers

    What is the mode of transmission for Streptococcus pyogenes?

    <p>Respiratory aerosols</p> Signup and view all the answers

    What severe condition may result from the rapid spread of Streptococcus pyogenes in the body?

    <p>Sepsis and septic shock</p> Signup and view all the answers

    What is the primary cause of Puerperal Sepsis?

    <p>Streptococcus pyogenes</p> Signup and view all the answers

    Which of the following complications is characterized by damage to heart valves due to autoimmune responses?

    <p>Acute rheumatic fever</p> Signup and view all the answers

    Which organism is associated with nephritogenic strains responsible for Acute Glomerulonephritis?

    <p>Streptococcus pyogenes</p> Signup and view all the answers

    What treatment or intervention is most critical for managing the complications sequential to a Streptococcal infection?

    <p>Immediate antibiotic therapy</p> Signup and view all the answers

    What symptom is NOT commonly associated with Acute Glomerulonephritis?

    <p>Chest pain</p> Signup and view all the answers

    What type of antibodies are formed due to cross-reacting human antigens after Streptococcus pyogenes infection?

    <p>Cross-reacting auto-antibodies</p> Signup and view all the answers

    How long after a streptococcal infection can Acute Glomerulonephritis develop?

    <p>1-3 weeks after recovery</p> Signup and view all the answers

    Study Notes

    Gram-Positive Cocci

    • Gram-positive cocci are spherical bacteria arranged in characteristic patterns
    • Gram-positive cocci can be divided into staphylococci and streptococci
    • Staphylococci form grape-like clusters while streptococci form chains

    Staphylococci

    • General features: spherical, Gram-positive, arranged in grape-like clusters, catalase-positive, non-motile, facultative anaerobic bacteria
    • Medically important species include Staphylococcus aureus (most important), Staphylococcus epidermidis and Staphylococcus saprophyticus
    • Classification based on coagulase enzyme: coagulase-positive (produce coagulase) and coagulase negative (do not produce coagulase)
      • Staphylococcus aureus is the example of coagulase-positive
      • Staphylococcus epidermidis and Staphylococcus saprophyticus are examples of coagulase-negative species
    • Coagulase: enzyme inducing plasma coagulation by activating prothrombin to thrombin and then fibrin
    • important virulence factors: Teichoic acid, Collagen-binding proteins (in attachment), and different exotoxins (proteases like collagenase and elastase, lipases, hyaluronidase, Pore-forming toxins like PV Leukocidin, Toxic Shock Syndrome Toxin (TSST), Exfoliative toxin(scalded skin syndrome) , Enterotoxin B)

    Staphylococcal Infections

    • Local skin infections (tissue destruction and pus formation): folliculitis, boils, wound infections, furuncles, carbuncles
    • Systemic infections (reach the blood stream): septicemia, endocarditis, osteomyelitis, meningitis, pneumonia, septic shock
    • Septic shock can be caused by Teichoic acid or TSST.

    Staphylococcus aureus

    • Epidemiology/Transmission: 30-50% of people carry in anterior nares, 5% in vaginas, spreading possible via hands, skin, throat and other surfaces
    • MRSA (Methicillin Resistant Staphylococcus aureus) common, VRSA appeared
    • important virulence factors: Teichoic acid, Collagen-binding proteins, Exotoxins and Exfoliative Toxin: involved in scalded skin syndrome and causes tissue damage, and Enterotoxin B involved in food poisoning.

    Other diseases caused by S. aureus

    • Non-pyogenic skin conditions: cellulitis and impetigo
    • Scalded skin syndrome(SST): epidermolytic toxins (exfoliative toxins) cleave desmogleins in superficial skin layers causing massive skin exfoliation; fever, large areas of skin slough, secondary infections, electrolyte imbalances can occur

    Staphylococcal Food Poisoning

    • Ingestion of food heavily contaminated with S. aureus strains containing enterotoxin B can result in self-limiting vomiting and watery diarrhea.
    • Enterotoxin B: a super-antigen that induces cytokine production in mesenteric lymph nodes after food ingestion
    • Cytokines stimulate vomiting center in the brain

    Staphylococcus epidermidis and Staphylococcus saprophyticus

    • Both coagulase-negative staphylococci
    • S. epidermidis is part of the normal human skin flora (90% of normal skin microbiota) found on skin and mucous membranes
    • It commonly infects intravenous catheters and prosthetic implants (e.g. prosthetic heart valves, vascular grafts, prosthetic joints (arthritis or osteomyelitis)
    • It can cause sepsis in neonates and peritonitis in patients with renal failure on peritoneal dialysis
    • S. saprophyticus causes urinary tract infections, especially in sexually active young women

    Streptococcus

    • Spherical, Gram-positive cocci that form chains
    • Catalase-negative
    • Are non-motile
    • Facultative anaerobes
    • Classified based on hemolytic activity: Alpha-hemolytic, Beta-hemolytic, Gamma-hemolytic
      • Alpha-hemolytic: green zone around colonies due to hemoglobin reduction to methemoglobin
      • Beta-hemolytic: clear zone around colonies due to complete lysis of red blood cells
      • Gamma-hemolytic: no change around colonies
    • Classification based on Lancefield Grouping: important CHO antigen of the cell wall (e.g. C carbohydrate)

    Streptococcus pyogenes (Beta-hemolytic/Group A)

    • Key pathogen
    • Commonly found in skin and throat
    • Important virulence factors: M protein (anti-phagocytic), capsule (anti-phagocytic, surface disguise), Teichoic acid(can cause toxic shock), Pore-forming toxins (hemolysins like Streptolysin), Pyogenic exotoxin A, (super-antigen, causing toxic shock)
    • Infections: Pharyngitis (strep throat), scarlet fever (rash, strawberry tongue), Otitis media, bronchitits, pneumonia (bacteremia, septic shock), meningitis, non-pyogenic skin infections (cellulitis and impetigo), toxic shock (systemic disease), Streptococcal gangrene (necrotizing fasciitis), Erysipelas, Puerperal sepsis (childbirth fever)
    • Post-Streptococcal diseases: Acute glomerulonephritis, acute rheumatic fever (immune reaction against streptococcal M protein), subcutaneous nodules, Sydenham’s chorea

    Post-Streptococcal diseases

    • Acute glomerulonephritis: inflammatory condition affecting glomeruli (kidneys) due to cross-reacting antibodies binding to human antigens
    • Acute rheumatic fever: inflammation of heart valves caused by immune response to streptococcal M protein and other antigens causing heart valve damage

    Other Streptococcus

    • Viridans streptococci: commonly found in the oropharynx
    • Streptococcus agalactiae: found in vagina and colon
    • Enterococci and anaerobic streptococci: found in the colon

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    Gram-Positive Cocci PDF

    Description

    This quiz explores the characteristics and classifications of Gram-positive cocci, focusing on staphylococci and streptococci. It discusses the unique arrangements, medically important species, and the significance of coagulase in bacterial classification. Test your knowledge about these essential microorganisms in microbiology.

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